Apparatus for processing molten metal

ABSTRACT

A gas cleaning system for hearth furnaces having means for injecting process fluids below the level of molten metal and means for adjusting air intake by means of dampers in the furnace or the gas flow system or adjustable gaps between the furnace and the gas cleaning system. The furnace may be operated in the full or partial combustion mode wherein suitably located dampers control air flow to obtain the desired degree of combustion. Control means adjusts the damper or gap in the event normal air flow is disturbed. Provision is made in the system for measuring the calorific value of the off-gases and recovery of those offgases having usable fuel capacity.

United States Patent [191 Baum et al.

n] 3,873,073 Mar. 25, 1975 [75] lnventors: Joerg P. Baum; Jai K. Pearce, both of Pittsburgh, Pa.

[73] Assignee: Pennsylvania Engineering Corporation, Pittsburgh, Pa.

221 Filed: June 25,1973 211 App1.No.:373,014

3,592,630 7/1971 Willet 75/60 3,706,549 12/1972 Knuppel et a1. 266/35 X 3,788,619 1/1974 Dortenzo 266/16 R13,763 7/1914 Albert 266/16 Primary ExaminerGerald A. Dost Attorney, Agent, or FirmFred Wiviott [57] ABSTRACT A gas cleaning system for hearth furnaces having means for injecting process fluids below the level of molten metal and means for adjusting air intake by means of dampers in the furnace or the gas flow system or adjustable gaps between the furnace and the gas cleaning system. The furnace may be operated in the full or partial combustion mode wherein suitably located dampers control air flow to obtain the desired degree of combustion. Control means adjusts the damper or gap in the event normal air flow is disturbed. ,fiambn 156166616 the systefirfdr' measuring the calorific value of 'the off-gases and recovery of those off-gases having usable fuel capacity.

43 Claims, 8 Drawing Figures PATENTEMmzSms sum 1 or '3 CONTROL FIG'J PMENTEB MAR 2 5 I975 sum 2 OF 3 JOEPZOU 1 APPARATUS FOR PROCESSING MOLTEN METAL BACKGROUND OF THE INVENTION Conventional open hearth furnaces are generally reverberatory wherein a burner is disposed on either side of the hearth for being alternately activated, and a regenerative chamber or checker is connected to the gas inlet at each end of the furnace for preheating incoming air and for recovering heat from the discharging gases. When the burners are alternated, the flow of gases through the furnace system is similarly alternated wherein incoming air is drawn over the checkers previously heated by discharged gases and the discharging gases are passed over the exit checkers. Open hearth furnaces are also normally provided with doors which are opened for charging and deslagging. Recently it has been proposed to modify open hearth furnaces by the inclusion of one or more tuyeres for injecting oxygen and other fluids below the level of molten metal. The use of submerged tuyeres, as well as the regenerative system and the charging doors make the application of gas cleaning systems to such open hearth furnaces difficult. For example, when the charging doors are opened, the gas cleaningsystem, which is preferably of the constant volume type, may be overloaded with a large amount of excess air. Moreover, if large amounts of air are allowed to enter the gas cleaning system-when the system is operating under partial combustion conditions, there is a possibility that enough oxygen will be present to react with the hot carbon monoxide in the off-gases to cause an explosion.

Another problem involved in the application of gas cleaning systems to open hearth type furnaces is the wide range of possible operating conditions. For example, the furnace may be operated in a full combustion mode wherein combustible off-gases are burned above the bath wherein the heat energy available in these gasesis employed in the furnace. On the other hand, the furnace off-gases may be only partially oxidized and recovered for their calorific value. In addition, the percentage' scrap-to-hotmetal of the metallic charge may vary from l00%. Such wide variations in scrap charging ratios provide substantial variations in the fur-. nace heat input requirements and in the off-gascomposition.

SUMMARYOF THE INVENTION A general object of this invention is to provide a gas cleaning system for a metallurgical furnace which is subject to large fluctuations in the amount of gas evolved from the melt or otherwise present in the furnace during a process cycle. Another object of the invention is to provide a gas cleaning system wherein the amount of oxygen in the system is maintained below the amount at which combustion of refining gases can occur.

Still another object of the invention is to provide a metallurgical system including a gas cleaning system wherein the oxygen is maintained at a level wherein combustion can be controlled.

A further object of the invention is to provide a gas cleaning system for metallurgical vessels wherein the volume of off-gases and intermixed air is held within the capability of the gas cleaning system.

An additional object of the invention is to provide a metallurgical furnace gas cleaning system operable under various combustion conditions and scrap-to-hot metal charging ratios.

A still further object of the invention is to provide a gas cleaning system which measures the calorific value of the gases passing therethrough and is adapted'for collection of useful fuel gases.

Yet another object of the invention is to provide a gas cleaning system which can be utilized with both fixed and tiltable furnaces.

How the foregoing and other more specific objects of the invention are achieved will be set forth in a more detailed description of the preferred embodiments of the invention taken in conjunction with the accompanying drawings.

Generally, the invention comprises providing a metallurgic'al vessel gas cleaning system having sensing devices for determining when excess air enters the system and for adjusting the same. In addition, gas analyzers are provided for measuring the calorific value of the gases entering the gas cleaning system, for altering the gas cleaning system flow path and for collection of those gases which are suitably high in calorific value so that the economic benefits of the fuel may be realized.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view illustrating a furnace with which the invention may be employed;

FIG. 2 schematically illustrates an open hearth furnace and the gas cleaning system according to the invention; and

FIG. 3 schematically illustrates an alternate embodiment of the invention; and

FIGS. 4-8 illustrate alternate embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 schematically illustrate a furnace 10 which may be employed with a gas system according to the invention. Furnace 10 generally includes a refractory shell 11 surrounded by a supporting framework generally designated by the reference numeral 12. The refractory shell or lining ll defines a vessel having a shallow hearth 14 for containing a bath of molten metal 15. One or more charging openings 17 are formed along one side of the furnace l0 and each is provided with a charging door 18 which may normally be raised and lowered when desired in any suitable manner such as by means of a motor operated hoist 21 mounted on frame 12. Thefurnace 10 itself may be mounted on stationary concrete or steel supports (not shown) or it may be mounted on rockers 22 whereby it may be tilted about an axis perpendicular to the plan of FIG. 1 for purposes of charging,pouring and deslagging.

A plurality of tuyeres 23 may extend through at least one side of the furnace 10 with their inner ends below the level of the bath 15. Tuyeres 23 may include two or more concentric pipes 23a and 23b wherein a first process gas, such as oxygen, may be blown through the inner pipe 23a and a hydrocarbon shielding fluid such as propane may be blown through the gap between the inner pipe 23a and the outer pipe 23b. As those skilled in the art will appreciate, the shielding gas prolongs refractory and tuyere life. In addition to oxygen and propane, other process gases such as argon and nitrogen may be blown through one or both of the tuyere pipes oxide, fluorspar, burnt lime and other materials may be entrained in the gas stream to provide the desired metallurgical reaction.

For purposes of illustrations, only one end of furnace is shown to be provided with an opening 25 and only a single burner 28 is provided through the other end 26. In normal operation of the furnace 10, it will typically be charged with scrap and hot metal which is then melted and/or preheated by means of the burner 28. The tuyeres 23 may also be employed during the preheat period by blowing fuel and oxygen into the furnace. After charging and the preheat period, the burner 28 will be turned off and the main furnace operation initiated. During waiting periods, deslagging and tapping inert gases such as nitrogen and argon are blown into the melt through both tuyere pipes 23a and 23b to maintain sufficient pressure within the tuyeres to maintain them free of metal. Also, when desulfurization is required, an inert gas such as argon or nitrogen is blown into the melt in this manner while lime is charged through the doors 17 or entrained as a powder in the gas stream. Refining is accomplished by the delivery of oxygen and other process gases and materials to the bath by means of the tuyeres 23..The oxygen reacts with impurities in the melt, such as carbon, phosphorous, silicon and manganese. Atthe end of the refining period, the carbon level of the melt may be determined in any suitable manner and then adjusted by the blowing of additional oxygen or by the introduction of carbon. The carbon may be in the form of a gas which is injectedinto the bath through the outer tuyere 4 peratureby exothermic reactions or the temperature may be lowered by the use of coolants.

As a result of the gases generated by the use of the burner 28, which typically employs a mixture of fuel oil or gas and air and the gas emanating from the bath during the oxygen blow, a substantial quantity of off-gas is discharged through opening 25. In accordance with the invention, the off-gases from the furnace are not discharged through checkers as is the case with conventional open hearth furnace installations, but instead the gases are conveyed to a gas cleaning system 30 which will be described below. For this purpose a short conduit 31 is mounted on furnace 10 in concentric surrounding relationship to opening 25. Disposed adjacent the remote end of conduit 31 is the horizontal end of an otherwise generally U-shaped conduit 33. Conduit burned before discharge to the atmosphere. On the v 33 is preferably formed of adjacently disposed water pipes through which cooling water is circulated when the apparatus is in operation. Conduit 33 is configured in the manner of a trap and may have a collection door 34 at its lower end for collecting the particulates which are driven downwardly at high velocity by the gas in which they are entrained. The change in gas direction brought about by the U-shaped configuration assists in accomplishing thispurpose. As seen in FIG. 2, a gap 35 exists between conduit 31 and the end 32 of conduit 33 which allows the furnace 10 to be tilted and also permits entry of some fixed amount of atmospheric air into conduit 33 and the ensuing gas cleaning system 30. If furnace 10 is fixed, no gap is required between conduits 31 and 33. I

having an adjustable throat 42 is coupled to receive the gases discharging from venturi 38 and a second separator 43 is coupled to the exit end of venturi 41. The water formed in the second separator 43 may be recirculates from sump 44 to venturi 38. The first venturi 39 is essentially a constant volume or low pressure drop device while the second venturi 41 may be a high pressure drop device which may function as an auxiliary pressure control for the gas cleaning system according to the invention. The two venturis 39 and 41 need not, of course, be placed on top of each other but could be connected in series in any manner known to the art.

A blower 45 connects the separator 43 to a discharge stack 46 having burner 47 at its upper end and a damper 48 intermediate its ends. A takeoff pipe 49 is connected at one end to stack 46 between damper 48 and blower 45. and the other end of pipe 49 is connected to water trap 51. A second damper 50 is disposed intermediate the ends of pipe 49.. A quantity of water 52 is disposed in water trap 51 to a level above the lower end of pipe 49 and a second pipe 53 is coupled at one end to trap 51 above the level of water 52 and at its other end to a suitable gas storage means not shown. It will be appreciated that whendamper 48is open and damper 50 is closed the off-gases entering stack 46 pass upwardly to burner 47whereupon any combustible components therein are oxidized or other hand, when damper 48 is closed and damper 50 is open, the off-gases'are diverted'through pipe 49 to water trap 51 from which they may bethen conducted through pipe 53 to suitable storage containers not shown. l

The dampers 48 and 50 are selectively controlled by servo motors 54 and 55, respectively, and which in turn are regulated by a'c'ontroller 57 which dictates alternate closing and opening of the dampers. Controller 57 is coupled to receive signals from a sensor 58 which extends into pipe 36. The sensor may be of any well known type which measures the chemical content and hence the calorific value of the gases, entering the venturi 38. For example, the sensor 58may include an oxygen partial pressure analyzer of any well known type such as the Oxysensor sold by the General Electric Company. In this device, an electricallpotential is developed between two electrodes immersed into media having different oxygen partial pressures and which are separated by an oxygen-ion conducting calcium stabilized zirconium oxide electrode. With a preset temperatre and a known reference gas oxygen partial pressure, the open cell voltage between the two gases can be used to calculate the oxygen partial pressure of the gas to be measured in accordance with the Nernst equation. In addition, sensor 58 may include an infrared sensor which may be connected in series with the oxygen partial pressure analyzer indicating the percentage of carbon monoxide, carbon dioxide and water vapor in the gas being 'analyzed. Any well known type of infrared gas analyzer may be employed such as the Mine Safety Appliance Company model 300 infrared analyzer. Signals functionally related to the oxygen partial pressure analysis and the percentages of C0, C0 and H 0 in the gas being analyzed are processed in the control 57 to actuate servo motors 54 and 55 when gas conditions dictate. If sensor 58 indicates that the gas is of sufficiently high calorific value as would normally be the case during the oxygen blowing period, controller 57 actuates servo motors 54 and 55 to close damper 48 and open damper 50 whereby the off-gases are collected. On the other hand, if the sensor 58 indicates that gases are of insufficient calorific value as would normally occur at the beginning and end of the process cycle, servo motors 54 and 55 are operated to open damper 48 and close damper 50 whereby the gases are burned and discharged as indicated above.

When the furnace is operated in its partial or incomplete combustion mode, the off-gases may contain about 25% carbon monoxide which is combustible or even explosive provided that adequate oxygen is available to support combustion. Accordingly, the oxygen level in the gas cleaning system should be maintained at a safe level which is 50% or below the amount required for sustaining combustion. This is accomplished according to another aspect of the invention. Specifically, pipe 33 has an opening 60 formed therein and adjacent which a damper 61 is pivotably mounted. The position of damper 61 relative to opening 60 determines the volume of air entering pipe 33 through opening 60. Damper 61 may be adjusted relative to opening 60 by means ofa servo motor 63 which in turn is adjustably positioned by a controller 64 to receive signals indicative of pressure within furnace l0 and from pressure responding device 66. Alternately, the pressure sensing device may be placed within pipe section 32. In the event furnace 10 is fixed so that there is no gap 35, the size of opening 60 and the adjustment of damper 61 will be such as to permit the inflow of the desired volume of oxygen.

nace (or in pipe 32 depending on placement of sensor 66). The electrical signals are then compared by controller 64 to reference signals in a manner well known in the art and controller 64 act-uates servo motor 63 which in turn adjusts damper 61 when the magnitude of an error signal reaches some predetermined value. It will also be noted that controller 64 may control the adjustable throat 42 of the second venturi 41 which as stated before functions to assure uniform pressure to the constant volume blower 45. Control of variable throat 42 is usually only required during the initial charging ancl preheating steps of the refining cycle since those steps are full combustion. During the period of the oxygen blow wherein there is less than full combustion, suitable regulation may be accomplished by damper 61 in pipe 33 as more fully explained hereafter.

During normal furnace operation, that is, when the doors 18 are closed, substantially all of the air entering the off-gas stream is that which is drawn through gap 35 and opening 60. Damper 61 and gap 35 are set such that a predetermined amount of air is emitted to pipe 33 along with the off-gases blowing therethrough. The amount of air is preferably limited to 50% or less of that which is required to support combustion.

When one or more of the furnace doors 18 are open, as may be required, for example, in a deslagging operation, pressure sensor 66 senses a drop in pressure within furnace l2. Sensor 66 thereupon delivers an electrical signal functionally related to the pressure drop to controller 64 which operates servo motor 63 for moving damper 61 toward a closed position relative to opening 60 in conduit 33. This reduces the amount of air which may enter through opening 61 to compensate for the increased volume of air now entering furnace 10 and exiting with the off-gases through the charging openings 17. The volume of air entering opening 60 is thus reduced so that the total amount of air flowing into gas cleaning system 30 is maintained preferably at a level below 50% of that which is required to support combustion. When the furnace charging doors 18 are again closed, increased pressure is again detected by sensor 66 which affects the operation of servo motor 63 by means of controller 64 whereby damper 61 is returned to its normally open position.

According to an alternate embodiment of the invention shown in FIG. 1, a motor of the reversing type is operative to open and close door 18 and is electrically interlocked with servo motor 63. This can be accomplished in any suitable manner such as by coupling controller 64 to themotor 70 energizing conductors 71. When reversing switch 72 is placed in a first closed position to couple motor 70 to source 73 in a first sense for opening door 18, servo motor 63 is operated to close damper 61. Similarly when switch 72 is placed in an alternate closed position to couple motor 72 to source 73 in an opposite sense for closing door 18, servo 63 is operated to open damper 61.

FIG. 2 further illustrates an alternate embodiment of the invention wherein an oxygen partial pressure analyzer is disposed in the conduit 36 and is connected by conductor 81 through oxygen analyzer 82 which in turn is connected tomotor controller 64. The analyzer 80 may be of the electrolytic type discussed above with respect to probe 58.

It will be appreciated that the gas evolved from the bath 15 varies over the metal treatment period and accordingly the air aspirated through the gap 35 and the damper 61 and by controlling the venturi throat opening 42. Priorto the blowing of oxygen, an inert gas, such as nitrogen, is blown through the bath 15. When the oxygen blow is commenced, the evolution of combustible gases will likewise commence. Analyzer 80 is operative to control the position of damper 61 in accordance with the percentage of oxygen in the off-gases. For example, during the initial portion of the oxygen blow, when the quantity of evolved gases is low, CO and H evolution from the bath 15 is relatively low. Air aspirated through the gap 35 and damper 61 permits full combustion to CO and 11 0 with the remainder of the gas passing to gas cleaning system being nitrogen. The mixture of C0 11 0 and N is inert and noncombustible. At this stage the gas acts like an inert plug which flows through the gas cleaning system 30 purging it of oxygen for combustion and then discharging from stack 46. The oxygen partial pressure sensor 80 detects when the stoichiometric combustion point of the gases is reached. At this point, damper 61 is partially closed and the safe capture of waste gases may be initiated without a danger of explosion.

More specifically, as the initial period of a heat progresses, the combined CO and H concentration of the evolved gases increases markedly and combined CO and H concentration decreases. Since the volume of gas flow in this initial period is set by the preset position of the variable venturi throat 42, air intake must necessarily be reduced at this time. The oxygen partial pressure sensor 80 detects the stoichiometric combustion point and thereby the absence of oxygen in the system and causes damper 61 to be partially closed to maintain the percentage of air within the system to a predetermined percentage of the total gas flow or about 50% of that required for stoichiometric combustion.

After the damper 61 has been positioned to provide the desired gas flow through the variable venturi throat 42 is used for finer operational corrections. The signals controlling the movement of the venturi throat 41 are based on furnace pressure which provides system sensitivity and minimizes pulsations of evolved gases through the air gap 35 to the atmosphere. Major fluctuations in flow rate are then corrected by the damper 61.

When the oxygen blow approaches its end point, the combined concentrations of CO and H in the off-gases decrease and those of CO +H O increase. The rate of gas flow at this time is controlled by the variable venturi throat 42 and damper 61'. As air is aspirated through the air gap 35 and damper 61, conditions for s'toichiometric combustion once again occurs. This condition is sensed by the oxygen partial pressure sensor 80 whic initiates the signal for further opening damper 61. In the event furnace is fixed, the gap 35 can be eliminated in which event,.the air inlet will be limited to damper 61.

FIG. 3 shows yet another embodiment of the apparatus for controlling the quantity of air provided to pipe 33. Here the gap 90 between conduit 35 and the inlet to pipe 33 is adjusted and may be used along or together with the damper of the type shown in FIG. 2 to regulate air addition. More specifically, a conduit member 91 is disposed between end 32 of conduit 33 and conduit 31 attached to furnace 11. The conduit 91 has a first end spaced from the end of furnace conduit 31 to provide the gap 90 therebetween. The other end of conduit 91 is telescopingly received within the inlet end 32 of gas cleaning system conduit 33. Conduit 91 may be mounted in any suitable manner for movement toward and away from conduit 31 for increasing and decreasing the size of gap 90. For example, conduit 91 may be mounted on rollers 93 which are in turn mounted on generally horizontal rails 94 mounted therebelow. Any suitable means may be provided for moving pipe section 91 horizontally on rails 94 such as a hydraulic cylinder96. A suitable source of hydraulic pressure 97 may be selectively coupled to the opposite sides of cylinder 96 through a reversing valve 98. Servo motor 99 is operative to selectively actuate valve 98 in accordance with signals from the controller and thereby to pressurize either of the opposite ends ofcylinder 96 to adjust the size of gap 94 in accordance with a pressure within vessel 10. Specifically, when door 18 is open to decrease the pressure within vessel 10 and indicating excess air entering the gas cleaning system, cylinder 96 will be pressurized so as to decrease the size of gap 90 while on the other hand when the door 19 is closed the opposite end of cylinder 96 will be pressurized to return conduit 91 to its initial position and thereby re-establish the initial size of gap 90.

As mentioned previously, a damper 61 may be used in conjunction with this embodiment of the invention,

8 in which case the initial large adjustments may be made by moving pipe conduit 91 while fine corrections may be made by use of the damper 61. Motor 63 cooperates with controller 64 as described in connection with FIG. 2. Placement of sensor 66 may be either in the furnace 10 or in conduit 91 as explained in conjunction with FIG. 2.

FIGS. 4 and 5 illustrate an alternate embodiment of the invention wherein the furnace 10 is operated in a full combustion system. Here a fan is coupled to the furnace through a port 81 for blowing combustion air into the furnace during the various furnace operations.

As a result, the combustible gases emanating from the bath 15 are oxidized prior to the delivery to the gas system 30. -In this embodiment, of course, gas storage is not employed. In addition, because of the delivery of air to the furnace 10 through port 81, an air intake gap is not necessary or desirable at the discharge port 25. Accordingly, the juncture between furnace exhaust conduit 31 and the gas cleaning system inlet conduit 32' is preferably closed..ln the event the furnace 10 is of the tilting type, the connection between conduits 31 and 32' should be flexible. For example, the flexible connection may comprise a water seal 82 having hood member 83 connected to the end of conduit 31' and extending downwardly past the end of conduit 32. In addition, a water container 85 extends upwardly from the end of conduit 32 and past the lower end of hood 83. A quantity of water 86 is disposed within the container 85 and above the level of the lower end of hood 83 to providea liquid seal between conduits 31 and 32. As seen in FIG. 4, when vessel 10 is tilted to tilt conduit 31, the lower end of hood 83 remainsbelow the level of the water,86 to maintain the seal between conduits 31' and 32'..

Referring again to FIG. .4, it can be seen that a damper 87 is provided between fan 80 and the inlet port 81. Damper 87 maybe positioned to control the flow of air into furnace 10 by means of a servo motor 63' coupled to control 64. The opening of furnace doors 18 will be sensed in'the manner-,discussed with respect to the embodiment of FIG. 2, such as for example, by means of a pressure measuring device 66 within vessel 10. Thus, when one of the doors .18. are opened motor 63' is actuated to partially closedamper 87 to reduce the amount of air entering port 81 and compensate for the air entering the furnace through the open door. When the door is reclosed, the motor 63' will reposition damper "-87 in itsnormal operating position. When doors 18 are closed, the position of damper 87 is normally controlled by an oxygen partial pressure sensor 80 and a series connected gas analyzer. 58, which may be of the infrared type. When appreciable quantities of CO or I-I are detected by analyzer 58 and sensor 80, motor 63' will be actuated to further increase the opening of damper 87. On the other hand, oxygen partial pressure sensor 80' will effect the movement of damper 87 toward a closed position when the percentage of excess oxygen exceeds a preselected level.

According to an alternate embodiment of the invention shown in FIG. 6, damper 87 is disposed in a vent conduit 90 coupled to fan 80 and in parallelism with furnace inlet port 81. The damper 87' is operable to vent a portion of the air provided at the outlet of fan 80 when the furnace doors are opened in the manner similar to that discussed with respect to the embodiment of FIG. 4.

A further embodiment of the invention is shown in FIG. 7 wherein a damper 92 is shown to be disposed in a wall of furnace 10 opposite the vent opening 25. The vent 92 is controlled by a motor 93 and control 64 in response to the opening doors 18 in a manner similar to that discussed with respect to the vent 87 in FIG. 3. A gas cleaning system such as that shown in FIG. 2 is coupled to pipe 32 of FIG. 7 wherein an exhaust fan (not shown in FIG. 7) will create a sufficient indraft through opening 81 to draw air into the furnace to combust at least a portion of the gases discharging from the bath 15. If it is desired to control the combustion of gases within the furnace 10 so as to maintain a predetermined temperature for various portions of the process cycle, a temperature measuring device 94 may be suitably located, such as for example, within the outlet 31. When used in a partial combustion system, the temperature measuring device 94 is connected to the controller 64 for positioning the damper 92 so as to provide sufficient combustion of the off-gases to maintain the desired temperature conditions. A second damper 61 is also provided in the gas cleaning system inlet pipe 32 to regulate the amount of additional air required to maintain substantially constant gas flow to the gas cleaning system (not shown). The damper 61 is positioned by motor 63 and controller 64 in a reverse relation to damper 92 so as to maintain the gas flow to the cleaning system substantially constant. If the damper 92 was employed in a complete combustion system, a closed discharge conduit arrangement is employed. In the latter event, dampe 92 is controlled in relation to the opening and closing of doors 18 in addition to the heat requirements of the furnace.

The invention may also be used with conventional open hearth furnaces having a burner and a port at each end, the latter of which leads to a slag pocket which in turn are connected to a regenerator.

FIG. 8 schematically illustrates another embodiment of the invention wherein a pipe 99 is coupled to the gas cleaning system inlet (not shown) and to the flues 100 and 101 of an open hearth furnace. Although the furnace and checkers are not shown in FIG. 8, those skilled in the art will appreciate that each of the flues land 101 are connected to one of a pair of furnace checkers which in turn are connected to vertical gas passages extending upwardly from slag pockets into the ends of the open hearth furnace. Suitable control valves or dampers 102 and 103 are disposed in flues 100 and 101 respectively to control the direction of the gas flow. In additiom air inlets 104 and 105 are respectively coupled to a blower fan 106through ducts 107 and 108 and valves 109 and 110. It will be appreciated that the dampers 102 and 103 and the valves 109 and 110 control the direction of gas flow through the system. For example, if damper 102 and valve 110 are open and damper 103 and valve 109 closed, air will flow through flue 101, its associated checkers and air uptake and into one end of the furnace (not shown) while hot gas will discharge through the waste gas downtake at the other end of the furnace, through the connected checkers and through flue 100, the open damper 102 and to the gas cleaning system inlet pipe 32. When a number of furnaces are coupled to a common gas cleaning system, a damper 112 may be provided in pipe 99 for controlling furnace pressure. In addition, a damper (not shown) may be provided in the furnace wall (not shown) for controlling combustion air flow. In any event, such dampers are controlled in the manner discussed above with respect to FIGS. 2 and 7. When a change in the direction of gas flow is desired, dampers 102 and 103 and valves 109 and will be reversed. In any event, the damper 112 is controlled in the manner shown in FIGS. 1-3.

Although only a few embodiments of the invention have been described, the invention is not to be limited thereby but is only to be limited by the scope of the claims appended hereto.

What is claimed is:

1. A metallurgical process system comprising:

a metallurgical vessel for containing a quantity of molten metal to be processed,

said vessel including first means for introducing reactants to said molten metal whereby substantial quantities of gases are evolved therefrom, an exit opening formed in said vessel for discharging said gases,

gas disposal means for receiving said gases,

second means for coupling said exit opening to said gas disposal means,

said second means including third means for controlling the amount of air admitted to said gas disposal means through said second means,

and fourth means respective to a change in air flow I conditions into said vessel and being operable to actuate said third means to adjust the amount of air admitted to said gas disposal means,

an access opening formed in said vessel, closable means operatively associated with said access opening and movable between open and closed positions for opening and closing said access opening whereby air is admitted into said vessel when said closable means is open,

said fourth means being operative to sense the positionof said closable means and operable to actuate said third means to decrease the amount of air admitted to the gas disposal means through said sec ond means when said closable means is open and for increasing the amount of air admitted through said second means when said closable means is closed. v

2. The system set forth in claim 1, wherein said first means includes tuyere means extending through said vessel and having an inner end disposed below the level of molten metal normally disposed within said vessel for injecting oxygen beneath the level of said metal.

3. The system set forth in claim 1 wherein said second means includes conduit means having a terminal end disposed a predetermined distance from said exit opening to provide a gap therebetween to permit the entrance of air into said second means.

4. The system set forth in claim 3 wherein said third 9 means comprises means for adjusting the gap between said terminal end of said second means and said exit opening to adjust the quantity of air entering said gap.

5. The system set forth in claim 4 wherein said second means has an opening therein, and said third means additionally comprises means for controlling the size of said opening to control the amount of air entering said second means therethrough.

6. The system set forth in claim 1 wherein said second means has an opening formed therein, said third means comprising means for controlling the size of said opening to control the amount of air entering said second means therethrough.

7. The apparatus set forth in claim 1 wherein said fourth means comprises pressure sensing means disposed within said vessel for sensing pressure changes therein.

8. The apparatus as claimed in claim 1 wherein said fourth means comprises pressure sensing means disposed within said second means for sensing pressure changes therein. 2

9. The apparatus set forth in claim 1 and including selectively operable means for moving said closable means between its open and closed positions and said fourth means being coupled to said selectively operable means for actuating said third means in response to movement of said closable means by said selectively operable means.

10. The apparatus set forth in claim 1 wherein said gas disposal means comprises a gas cleaning system.

11. The apparatus as claimed in claim wherein said gas cleaning system includes a first low pressure drop venturi scrubber coupled to said second means nd a s ond. entur s rq zbsr .har asa @Qi throat coupled to said first venturi scrubber for r e gu lating the pressure of gas exiting the separator.

12. The apparatus set forth in claim '1 wherein said fourth means includes oxygen sensing means disposed in said second means for sensing the percentage of oxygen in the gases flowing therein, said oxygen sensing means being coupled to said third means to effect a reduction in the air entering said second means when the percentage of oxygen in the gases flowing in said second means reaches a predetermined value.

13. The system set forth in claim 1 wherein said vessel comprises an open hearth furnace having heating means provided in one end thereof, said exit opening being disposed in the other end thereof.

14. The system set forth in claim 13 wherein said first means includes tuyere means extending through said vessel and having an inner end disposed below the level of molten metal normally disposed within said'vessel for injecting oxygen beneath the level of said metal.

15. The system set forth in claim 14 wherein said tuyere means includes an inner pipe means coupledtgreceive oxygen and to "inject the same into said meta l and a second pipe means surrounding said first pipe means for receiving a shielding fluid and for injecting the m i qsailnst l asybsiantial y www. 19- ing relation to said oxygen.

16. The system set forth inclaim 15 wherein said second means includes conduit means having a terminal end disposed a predetermined distance from said exit opening to provide a gap therebetween to permit the entrance of air into said second means.

17. The system set forth in claim 16 wherein said third means comprises means for adjusting the gap between said terminal end of said second means and said exit opening to adjust the quantity of air entering said gap.

18. The system set forth in claim 16 wherein said second means has an opening therein, and said third means additionally comprises means for controlling the size of said opening to control the amount of air entering said second means therethrough.

19. The apparatus set forth in claim 18 wherein said fourth means includes oxygen sensing means disposed in said second means for sensing the percentage of oxy- 12 gen in the gases flowing therein, said oxygen sensing means being coupled to said third means to effect a reduction in the air entering said second means when the percentage of oxygen and the gases flowing in said second means reaches a predetermined value.

20. The apparatus as claimed in claim 19 wherein said gas disposal means is a gas cleaning system and said fourth means comprises pressure sensing means disposed within said second means for sensing changes in pressure within said second means.

21. The apparatus set forth in claim 19 wherein said gas disposal means is a gas cleaning system and said fourth means comprises pressure sensing means disposed within said vessel for sensing changes in pressure within said vessel.

22. The apparatus as claimed in claim 21 wherein said gas cleaning system includes a first low pressure drop venturi separator coupled to said second means and a second venturi separator having an adjustable throat coupled to said first venturi separator for regulating the pressure of gas exiting the separator.

23. The system set forth in claim 21 wherein said third means comprises means coupled to said vessel for admitting air thereto above the level of said molten metal to effect the combustion of gases in said vessel.

24. The system setforth in claim 23 and including means associated with saidthird means to controlling the flow of air to said vessel.

25. The system set forth in claim 24 wherein said vessel has a vent opening for discharging gases therefrom and a gas cleaning system coupled to said vent opening.

26. The system set forth in claim 25 wherein said vessel comprises an open hearth furnace having heating means provided in at least one side thereof, said vent opening being displaced from said heating means, said first means includes tuyere means extending through said vessel and having an inner end disposed below the levelof molten metal normally, disposed within said vessel for' injecting oxygen beneath the level of said metal, said tuyere means includes an inner pipe means 561156310 receive 'oxygen aridf to inject the same into said metal and a second pipe means surrounding said first pipe means for receiving a shielding gas and for injecting the same into said metal in a substantially surrounding relation to said oxygen.

27.,The system set forth in claim 26 and including an opening formed in said vessel and spaced from said vent opening, said third means including means for controlling the volume of air entering said opening.

28. The apparatus set forth in claim 27 wherein said fourth means comprises pressure sensing means disposed within said vesselfor sensing changes in pressure within said vessel. I

29. The apparatus as claimed in claim 28' wherein said fourth means comprises pressure sensing means disposed within said second means for sensing changes in pressure within said second means.

30. The system set forth in claim 29 and includin means coupling said vent opening to said gas cleaning system and having a second air admitting opening therein, and means for controlling the size of said second opening to control the amount of air entering said gas cleaning system therethrough.

31. An open hearth furnace having heating means provided in at least one side thereof, a vent opening formed in said vessel for discharging gases therefrom,

a second opening formedin said vessel and spaced from said vent opening.

air control means coupled to said second opening for admitting air thereto above the level of said molten metal to effect the combustion of gases in said vessel, and including means for controlling the volume of air flow to said vessel and through said second opening.

pressure sensing means disposed within one of said vessel or gas cleaning system for sensing changes in pressure within said vessel,

a gas cleaning system, coupling means for coupling said ventopening to said gas cleaning system and having a third air admitting opening therein, and means for controlling the size of said t hird opening to control the amount of air entering said gas cleaning system therethrough, and

oxygen sensing means disposed in said coupling means for sensing the percentage of oxygen in the gases flowing therein, said oxygen sensing means being coupled to said air control means to effect a reduction in the air entering said vesselwhen the percentage of oxygen in the gases flowing in said second means reaches a predetermined value.

32. The apparatus as claimed in claim 31 wherein said gas cleaning system includes a first low pressure drop venturi separator coupled to said second means and a second venturi separator having an adjustable throat coupled to said first venturi separator for regulating the pressure of gas exitingthe separator.

33. The apparatus set forth in claim 2 wherein said vessel includes charging door means, said door means including at least one charging door and operating means coupled to said door for effecting movement of the same between open and closed positions, said fourth means being coupled to said charging door means and being responsive to theposition thereof.

34. A metallurgical process system comprising:

a metallurgical vessel for containing a quantity of molten metal to be processed,

said vessel includingfirst means for introducing reactants to said molten metal whereby substantial quantities of gases are evolved therefrom, an exit opening formed in said vesselfor discharging said gases,

gas disposal means for receiving said gases,

second means for coupling said exit opening to said gas disposal means,

gas delivery means coupled to said vesselfor delivering oxygen containing gas thereto and above the level of said molten metal for oxydizing combustable gases emanating from said molten metal,

14 third means coupled to said gas delivery means for controlling the amount of oxygen containing gas admitted to said vessel,

an access opening formed in said vessel, closable means operatively associated with said access opening and movable between open and closed positions for opening and closing said access opening whereby air is admitted into said vessel when said closable means is open,

fourth means operative to sense changes in the position of said closable means and operable to actuate said third means to decrease the amount of oxygen containing gas admitted to the vessel through said gas delivery means when said closable means is open and for increasing the amount of said gas admitted through said gas delivery means when said closable means is closed.

35. The system set forth in claim 34 wherein said vessel has a vent opening for discharging gases therefrom and a gas cleaning system coupled to said vent opening.

36. The system set forth in claim 35 wherein said vessel comprises an open hearth furnace having heating means provided in at least one side thereof, said vent opening being displaced from said heating means, said first means includes tuyere means extending through said vessel and having an inner end disposed below the level of molten metal normally disposed within said vessel for injecting oxygen beneath the level of said metal, said tuyere means includes an inner pipe means coupled to receive oxygen and to inject the same into said metal and a second pipe in a ris surrounding said first pipe means for receiving a shielding gas and for injecting the same into said metal in a substantially surrounding relation to said oxygen. g

37. The system set forth in claim 36 wherein said gas delivery means includes an opening formed in said vessel and spaced from said vent opening, said third means including means for controlling the volume of air entering said opening.

38. The apparatus set forth in claim 37 wherein said fourth means comprises pressure sensing means disposed within said vessel for sensing changes in pressure within said vessel. v

39. The apparatus as claimed in claim 37 wherein said fourth means comprises pressure sensing means disposed within said second means for sensing changes in pressure within said second means.

40. The system set forth in claim 37 wherein said fourth means includes pressure sensing means disposed in one of said vessel and second means for sensing changes in pressure therein and including means coupling said vent opening to said gas cleaning system and having a second air admitting opening therein, and means for controlling the size of said second opening to control the amount of air entering said gas cleaning system therethrough.

41. The apparatus set forth in claim 37 wherein said fourth means includes oxygen sensing means disposed in said second means for sensing the percentage of oxygen in the gases flowing therein, said oxygen sensing means being coupled to said third means to effect a reduction in the air entering said vessel when the percentage of oxygen in the gases flowing in said second means reaches a predetermined value.

42. The apparatus as claimed in claim 41 wherein said gas cleaning system includes a first low pressure drop venturi separator coupled to said second means and a second venturi separator having an adjustable r a s l to Said f rst vsntsti pw rf re s: lating the pressure of .gas exiting the second separator.

43. A metallurgical process system comprising: a metallurgical vessel for containing a quantity of molten metal to be processed, said vessel including first means for introducing reactants to said molten metal whereby substantial quantities of gases are evolved therefrom, an exit opening formed in said vessel for discharging said gases, gas disposal means for receiving said gases, second means for coupling said exit opening to said gas disposal means, third means for controlling the amount of air admitted to one of said vessel and gas disposal means, and'fourth means responsive to a change in air flow conditions into said vessel and being operable to actuage said third means to adjust the amount of air admitted to the one of said vessel and gas disposal means,

an access opening formed in said vessel, closable means operatively associated with said access opening and movable between open and closed positions for opening and closing said access opening whereby air is-admitted to said vessel when said closable means is open,

said fourth means operative to sense changes in the position of said closable means and'operable to actuate said third means to decrease the amount of air admitted to the vessel through said gas delivery,

said vessel comprising an open hearth furnace having a pair of spaced apart vent openings and tuyere means below the expected level of metal in said vessel,

conduit means connected to each of said vent openings, and valve means for selectively coupling one of said conduit means to a source of air and'the other of said conduit means to a gas cleaning systern.

UNITED STATES PATENT OFFICE I CETIFICATE 0F CORRECTION Patent No. 8 073 Dated M r h 25, 1975 Inventor(s) Joerg P. Baum et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 1, Column 10, line 28, change "respeccive' to -resp0nsive.,

Signed and Sealed this second 133) OF September 1975 [SEAL] Arrest" RUTH C. MASON C. MARSHALL DANN AIHSII'HX ()f/YCW (nmmissiuner nflutcnm and Trademarks 

1. A metallurgical process system comprising: a metallurgical vessel for containing a quantity of molten metal to be processed, said vessel including first means for introducing reactants to said molten metal whereby substantial quantities of gases are evolved therefrom, an exit opening formed in said vessel for discharging said gases, gas disposal means for receiving said gases, second means for coupling said exit opening to said gas disposal means, said second means including third means for controlling the amount of air admitted to said gas disposal means through said second means, and fourth means respective to a change in air flow conditions into said vessel and being operable to actuate said third means to adjust the amount of air admitted to said gas disposal means, an access opening formed in said vessel, closable means operatively associated with said access opening and movable between open and closed positions for opening and closing said access opening whereby air is admitted into said vessel when said closable means is open, said fourth means being operative to sense the position of said closable means and operable to actuate said third means to decrease the amount of air admitted to the gas disposal means through said second means when said closable means is open and for increasing the amount of air admitted through said second means when said closable means is closed.
 2. The system set forth in claim 1, wherein said first means includes tuyere means extending through said vessel and having an inner end disposed below the level of molten metal normally disposed within said vessel for injecting oxygen beneath the level of said metal.
 3. The system set forth in claim 1 wherein said second means includes conduit means having a terminal end disposed a predetermined distance from said exit opening to provide a gap therebetween to permit the entrance of air into said second means.
 4. The system set forth in claim 3 wherein said third means comprises means for adjusting the gap between said terminal end of said second means and said exit opening to adjust the quantity of air entering said gap.
 5. The system set forth in claim 4 wherein said second means has an opening therein, and said third means additionally comprises means for controlling the size of said opening to control the amount of air entering said second means therethrough.
 6. The system set forth in claim 1 wherein said second means has an opening formed therein, said third means comprising means for controlling the size of said opening to control the amount of air entering said second means therethrough.
 7. The apparatus set forth in claim 1 wherein said fourth means comprises pressure sensing means disposed within said vessel for sensing pressure changes therein.
 8. The apparatus as claimed in claim 1 wherein said fourth means comprises pressure sensing means disposed within said second means for sensing pressure changes therein.
 9. The apparatus set forth in claim 1 and including selectively operable means for moving said closable means between its open and closed positions and said fourth means being coupled to said selectively operable means for actuating said third means in response to movement of said closable means by said selectively operable means.
 10. The apparatus set forth in claim 1 wherein said gas disposal means comprises a gas cleaning system.
 11. The apparatus as claimed in claim 10 wherein said gas cleaning system includes a first low pressure drop venturi scrubber coupled to said second means and a second venturi scrubber having an adjustable throat coupled to said first venturi separator for regulating the pressure of gas exiting the separator.
 12. The apparatus set forth in claim 1 wherein said fourth means includes oxygen sensing means disposed in said second means for sensing the percentage of oxygen in the gases flowing therein, said oxygen sensing means being coupled to said third means to effect a reduction in the air entering said second means when the percentage of oxygen in the gases flowing in said second means reaches a predetermined value.
 13. The system set forth in claim 1 wherein said vessel comprises an open hearth furnace having heating means provided in one end thereof, said exit opening being disposed in the other end thereof.
 14. The system set forth in claim 13 wherein said first means includes tuyere means extending through said vessel and having an inner end disposed below the level of molten metal normally disposed within said vessel for injecting oxygen beneath the level of said metal.
 15. The system set forth in claim 14 wherein said tuyere means includes an inner pipe means coupled to receive a reactive gas and to inject the same into said metal and a second pipe means surrounding said first pipe means for receiving a shielding fluid and for injecting the same into said metal in a substantially surrounding relation to said reactive gas.
 16. The system set forth in claim 15 wherein said second means includes conduit means having a terminal end disposed a predetermined distance from said exit opening to provide a gap therebetween to permit the entrance of air into said second means.
 17. The system set forth in claim 16 wherein said third means comprises means for adjusting the gap between said terminal end of said second means and said exit opening to adjust the quantity of air entering said gap.
 18. The system set forth in claim 16 wherein said second means has an opening therein, and said third means additionally comprises means for controlling the size of said opening to control the amount of air entering said second means therethrough.
 19. The apparatus set forth in claim 18 wherein said fourth means includes oxygen sensing means disposed in said second means for sensing the percentage of oxygen in the gases flowing therein, said oxygen sensing means being coupled to said third means to effect a reduction in the air entering said second means when the percentage of oxygen and the gases flowing in said second means reaches a predetermined value.
 20. The apparatus as claimed in claim 19 wherein said gas disposal means is a gas cleaning system and said fourth means comprises pressure sensing means disposed within said second means for sensing changes in pressure within said second means.
 21. The apparatus set forth in claim 19 wherein said gas disposal means is a gas cleaning system and said fourth means comprises pressure sensing means disposed within said vessel for sensing changes in pressure within said vessel.
 22. The apparatus as claimed in claim 21 wherein said gas cleaning system includes a first loW pressure drop venturi separator coupled to said second means and a second venturi separator having an adjustable throat coupled to said first venturi separator for regulating the pressure of gas exiting the separator.
 23. The system set forth in claim 21 wherein said third means comprises means coupled to said vessel for admitting air thereto above the level of said molten metal to effect the combustion of gases in said vessel.
 24. The system set forth in claim 23 and including means associated with said third means to controlling the flow of air to said vessel.
 25. The system set forth in claim 24 wherein said vessel has a vent opening for discharging gases therefrom and a gas cleaning system coupled to said vent opening.
 26. The system set forth in claim 25 wherein said vessel comprises an open hearth furnace having heating means provided in at least one side thereof, said vent opening being displaced from said heating means, said first means includes tuyere means extending through said vessel and having an inner end disposed below the level of molten metal normally disposed within said vessel for injecting oxygen beneath the level of said metal, said tuyere means includes an inner pipe means coupled to receive a reactive gas and to inject the same into said metal and a second pipe means surrounding said first pipe means for receiving a shielding gas and for injecting the same into said metal in a substantially surrounding relation to said reactive gas.
 27. The system set forth in claim 26 and including an opening formed in said vessel and spaced from said vent opening, said third means including means for controlling the volume of air entering said opening.
 28. The apparatus set forth in claim 27 wherein said fourth means comprises pressure sensing means disposed within said vessel for sensing changes in pressure within said vessel.
 29. The apparatus as claimed in claim 28 wherein said fourth means comprises pressure sensing means disposed within said second means for sensing changes in pressure within said second means.
 30. The system set forth in claim 29 and including means coupling said vent opening to said gas cleaning system and having a second air admitting opening therein, and means for controlling the size of said second opening to control the amount of air entering said gas cleaning system therethrough.
 31. An open hearth furnace having heating means provided in at least one side thereof, a vent opening formed in said vessel for discharging gases therefrom, said vent opening being displaced from said heating means. tuyere means extending through said vessel and having an inner end disposed below the level of molten metal normally disposed within said vessel for injecting oxygen beneath the level of said metal, said tuyere means including an inner pipe means coupled to receive a reactive gas and to inject the same into said metal and a second pipe means surrounding said first pipe means for receiving a shielding gas and for injecting the same into said metal in a substantially surrounding relation to said reactive gas, a second opening formed in said vessel and spaced from said vent opening. air control means coupled to said second opening for admitting air thereto above the level of said molten metal to effect the combustion of gases in said vessel, and including means for controlling the volume of air flow to said vessel and through said second opening. pressure sensing means disposed within one of said vessel or gas cleaning system for sensing changes in pressure within said vessel, a gas cleaning system, coupling means for coupling said vent opening to said gas cleaning system and having a second air admitting opening therein, and means for controlling the size of said second opening to control the amount of air entering said gas cleaning system therethrough, and oxygen sensing means disposed in said coupling means for sensing the percentage of oxygen in the gases flowing therein, said oxygen sensing means bEing coupled to said air control means to effect a reduction in the air entering said vessel when the percentage of oxygen in the gases flowing in said second means reaches a predetermined value.
 32. The apparatus as claimed in claim 31 wherein said gas cleaning system includes a first low pressure drop venturi separator coupled to said second means and a second venturi separator having an adjustable throat coupled to said first venturi separator for regulating the pressure of gas exiting the separator.
 33. The apparatus set forth in claim 1 wherein said vessel includes charging door means, said door means including at least one charging door and operating means coupled to said door for effecting movement of the same between open and closed positions, said fourth means being coupled to said charging door means and being responsive to the position thereof.
 34. A metallurgical process system comprising: a metallurgical vessel for containing a quantity of molten metal to be processed, said vessel including first means for introducing reactants to said molten metal whereby substantial quantities of gases are evolved therefrom, an exit opening formed in said vessel for discharging said gases, gas disposal means for receiving said gases, second means for coupling said exit opening to said gas disposal means, gas delivery means coupled to said vessel for delivering oxygen containing gas thereto and above the level of said molten metal for oxydizing combustable gases emanating from said molten metal, third means coupled to said air delivery means for controlling the amount of oxygen containing gas admitted to said vessel, an access opening formed in said vessel, closable means operatively associated with said access opening and movable between open and closed positions for opening and closing said access opening whereby air is admitted into said vessel when said closable means is open, fourth means operative to sense changes in the position of said closable means and operable to actuate said third means to decrease the amount of oxygen containing gas admitted to the vessel through said gas delivery means when said closable means is open and for increasing the amount of said gas admitted through said gas delivery means when said closable means is closed.
 35. The system set forth in claim 34 wherein said vessel has a vent opening for discharging gases therefrom and a gas cleaning system coupled to said vent opening.
 36. The system set forth in claim 35 wherein said vessel comprises an open hearth furnace having heating means provided in at least one side thereof, said vent opening being displaced from said heating means, said first means includes tuyere means extending through said vessel and having an inner end disposed below the level of molten metal normally disposed within said vessel for injecting oxygen beneath the level of said metal, said tuyere means includes an inner pipe means coupled to receive a reactive gas and to inject the same into said metal and a second pipe means surrounding said first pipe means for receiving a shielding gas and for injecting the same into said metal in a substantially surrounding relation to said reactive gas.
 37. The system set forth in claim 36 wherein said gas delivery means includes an opening formed in said vessel and spaced from said vent opening, said third means including means for controlling the volume of air entering said opening.
 38. The apparatus set forth in claim 37 wherein said fourth means comprises pressure sensing means disposed within said vessel for sensing changes in pressure within said vessel.
 39. The apparatus as claimed in claim 37 wherein said fourth means comprises pressure sensing means disposed within said second means for sensing changes in pressure within said second means.
 40. The system set forth in claim 37 wherein said fourth means includes pressure sensing means disposed in one of said vessel and second means for sensing changes iN pressure therein and including means coupling said vent opening to said gas cleaning system and having a second air admitting opening therein, and means for controlling the size of said second opening to control the amount of air entering said gas cleaning system therethrough.
 41. The apparatus set forth in claim 37 wherein said fourth means includes oxygen sensing means disposed in said second means for sensing the percentage of oxygen in the gases flowing therein, said oxygen sensing means being coupled to said third means to effect a reduction in the air entering said vessel when the percentage of oxygen in the gases flowing in said second means reaches a predetermined value.
 42. The apparatus as claimed in claim 41 wherein said gas cleaning system includes a first low pressure drop venturi separator coupled to said second means and a second venturi separator having an adjustable throat coupled to said first venturi separator for regulating the pressure of gas exiting the separator.
 43. A metallurgical process system comprising: a metallurgical vessel for containing a quantity of molten metal to be processed, said vessel including first means for introducing reactants to said molten metal whereby substantial quantities of gases are evolved therefrom, an exit opening formed in said vessel for discharging said gases, gas disposal means for receiving said gases, second means for coupling said exit opening to said gas disposal means, third means for controlling the amount of air admitted to one of said vessel and gas disposal means, and fourth means responsive to a change in air flow conditions into said vessel and being operable to actuage said third means to adjust the amount of air admitted to the one of said vessel and gas disposal means, an access opening formed in said vessel, closable means operatively associated with said access opening and movable between open and closed positions for opening and closing said access opening whereby air is admitted to said vessel when said closable means is open, said fourth means operative to sense changes in the position of said closable means and operable to actuate said third means to decrease the amount of air admitted to the vessel through said gas delivery, said vessel comprising an open hearth furnace having a pair of spaced apart vent openings and tuyere means below the expected level of metal in said vessel, conduit means connected to each of said vent openings, and valve means for selectively coupling one of said conduit means to a source of air and the other of said conduit means to a gas cleaning system. 